NEW YORK (Reuters) - Oil production in North Dakota's Bakken shale stayed flat in January after falling sharply the month before, according to independent data that illustrate how this winter's bitter cold put a freeze on the world's fastest-growing oil patches.

Although December's extraordinary chill gave way to relatively warmer weather last month, Bakken output hovered just below 860,000 barrels-per-day, according to calculations by LCI Energy Insight, a Texas-based energy intelligence firm.

In December, Bakken oil production fell by nearly 50,000 bpd from a record just over 910,000 bpd in November, the largest drop since state records began, according to North Dakota Industrial Commission data this month.

The LCI figures, based on historical well production data and natural gas pipeline flows in North Dakota and Montana, are the first to show the full impact of winter weather on oil output, a trend that brought new seasonal uncertainty to oil markets in recent years.

Growth in the larger Eagle Ford shale in south Texas also ground to a halt at around 1.1 million bpd, according to the LCI data, which was made available to Reuters.

Parts of North Dakota had the third coldest December on record, so frigid, according to local papers, that diesel fuel froze in truck tanks. In January, it was the wind that forestalled the drilling and hydraulic fracturing operations that are necessary to keep output growing.

"December was very cold and January was warmer but windy," said Bill Abeling, a meteorologist with the National Oceanic and Atmospheric Administration in Bismarck, North Dakota. Peak wind speeds were above 35 miles per hour for a third of the month in Williston, the heart of the oil boom, Abeling added.

Although companies often cut back on fracking operations during the winter months due to operational issues, the impact was greater this year due to the severe conditions.

In addition, the weather in the northern Midwest state is wielding a greater influence on the oil market, forcing oil traders to adjust to a new dynamic. U.S. oil markets cannot overlook the loss of 50,000 bpd of Bakken crude just as winter heating fuel demand peaks, traders say.

Still, it is likely to be a temporary lull in the otherwise upward trajectory of the Bakken region, whose bounty turned North Dakota into the country's No. 2 oil-producing state. Regulators expect the backlog of wells waiting on completion, numbering 635 in December, to be up and running by May.

"In spite of the weather declines experienced in January, oil production from shale oil wells increased 30 percent from January 2013 after increasing almost 60 percent the year before," said George Lippman, president of LCI.

FREEZING OIL

Bakken oil output has regularly dropped or stalled during the winter months, only to race ahead until spring, when flooding sometimes crimps it again.

Natural gas markets have long been accustomed to winter supply constraints due to so-called well "freeze-offs", where frozen vapors block the flow of natural gas from a wellhead.

It is a newer, and different, phenomenon for oil markets, one felt far beyond North Dakota this year.

Oil production in the Eagle Ford of Texas, which was also hit by unseasonably cold weather, was flat at 1.12 million bpd in January versus the month before, after declining by a small 10,000 bpd in December, the LCI data show.

That was only the second monthly decline since heavy drilling began there. Output had been racing ahead by some 30,000 bpd per month, LCI data show.

By comparison, oil production in the Wolfcamp and Bone Springs shale plays of the Permian basin were flat in December and rose by a combined 11,000 bpd in January, according to LCI's projections.

The full effects of January's weather will not be clear until state regulators release official monthly production figures in several weeks' time.

LCI uses real-time natural gas pipeline flow data, modeled against historical well-by-well oil output figures, to forecast liquid production up to a month before official data is available. Big oil producers only release their data on a quarterly basis.

Meanwhile, the weather problems have helped keep wholesale price differentials for Bakken crude at a narrow discount against the U.S. oil futures contract, weighing on the market incentive to ship the oil to refiners on the East and West Coasts.

Bakken oil for delivery at Clearbrook, Minnesota traded between $1.65 and $3.50 a barrel under the front-month U.S. oil futures contract in January, compared with $15-a-barrel discounts against futures in early November.

WARMER BUT WINDY

North Dakota was slammed with four snowstorms and five windstorms in December, which slowed drilling and well completion work, the state oil and gas regulator said.